\begin{tikzpicture}[
    node distance = 2cm and 2cm,
    N/.style = {circle, draw, font=\Large, minimum size=1.1em},
    every edge/.style = {draw, -> , semithick, shorten >=2pt},
    every edge quotes/.style = {auto=right, inner sep=2pt}
    ]
    \node [N] (1) at (0,0) [label=left:{+}] {1};
    \node [N] (2) [right of =1] {2};
    \node [N] (3) [right of =2] {3};
    \node [N] (4) [right of =3] [label=right:{-}] {4};
    
    \path (1) edge [->] node [above] {a} (2)
    (2) edge [->] node [above] {b} (3)
    (3) edge [->] node [above] {c} (4)
    (2) edge [bend left] node [above] {$\varepsilon$} (4) %两个节点之间 长 上
    (1) edge [bend right] node [below] {$\varepsilon$} (2) %两个节点之间
    (2) edge [bend right] node [above] (e1) {$\varepsilon$} (1) %两个节点之间  上
    (3) edge [bend right] node [below] {$\varepsilon$} (4); %两个节点之间
    
\end{tikzpicture}
	
